The primary objective is to determine the effect of Aredia on bone loss associated with androgen deprivation. Hormonal therapy is the standard treatment for men with prostate cancer that has spread beyond the prostate. One of the side effects of hormonal therapy is osteoporosis or thinning of the bones. Osteoporosis may result in bone fractures and pain. Aredia is effective at preventing osteoporosis that results from female menopause or treatment with some medications. The effect of Aredia on ostoeporosis that results from hormonal therapy for prostate cancer is not known. The trial will include men with prostate cancer who are about to begin hormonal therapy. Prior to starting hormonal therapy, study participants will be randomized to standard care or treatment with Aredia every three months for two years. In addition to routie medical appointments, study participation will require eight outpatient visits for special testing over two years. The following tests will be performed dduring the trial: physical examinations, medical history, x-rays of bones (bone densitometry and scans), blood and urine tests.